Uses for trivalent thallium compounds, i.e., thallic compounds, are well documented in the chemical and patent literature. Their uses as oxidizing agents is described, for example, in Rizkalla, et al, U.S. Pat. No. 4,058,542, which not only summarizes prior uses for trivalent thallium but describes and claims therein the conversion of monovalent thallium compounds to a trivalent thallium compound in a liquid medium with molecular oxygen in the presence of a Group VIII noble metal and in the presence of a heterocyclic tertiary amine as promoter. Such process requires the use of molecular oxygen, high pressures, and heterocyclic amine promoters which, if carried along to subsequent reaction steps, could contaminate or interfere with the production or purity of other more valuable products of the overall process.
Other thallium (I) to thallium (III) oxidation procedures are known. For example, Japanese Kokai 74 30,291 (1974) describes the oxidation of thallous salts with oxygen in the presence of fatty acid salts of alkali or alkaline earth metal salts, and chloride or bromides of the metals in the presence or absence of copper or iron salts.
Japanese Kokai 74 13,104 describes the preparation of olefin oxides by oxidation of C.sub.3 to C.sub.5 -aliphatic olefins, said olefin oxidation being effected by the use of air (or oxygen) oxidized liquids comprising (a) thallous salts, (b) aliphatic acid salts or alkali or alkaline earth metals, (c) halides of alkali or alkaline earth metals and, optionally, (d) halides or aliphatic acid salts of copper or iron. A similar disclosure is found in Netherlands Application 6,505,487 (1965).
Also, Japanese Kokai 74 14,416 (1974) discloses the oxidation of thallous acetate to thallic acetate in about 50 percent yield with manganese dioxide. Thus, 3.9 weight parts of thallous acetate, 1.3 weight parts of manganese dioxide, and 100 ml of acetic acid was boiled for five hours to give 0.066 mole/liter of thallium III ion.
U.S. Pat. No. 3,479,262 (1969) describes the oxidation of thallium (I) to thallium (III) ions using cerium (IV) ions as the oxidizing agent in the presence of a noble metal catalyst. Such thallium (III) ion product is then used to oxidize olefins.
The above-exemplified prior art oxidation procedures all require high reaction temperatures (usually boiling), sometimes high pressures and/or long reaction times. Also, the resulting thallium (III) solutions are usually obtained in an aqueous solution containing strong acids (such as hydrochloric acid) which make such thallium (III) ion solutions of little value for some organic chemical conversion processes such as oxidation of enol ethers or some olefin oxidation uses. The above-referenced thallium (I) acetate to thallium (III) acetate using manganese dioxide (Japanese Kokai 74 14,416) requires long reaction times and vigorous conditions, which, in fact, destroy some of thallium (III) once it forms. Also, the manganese dioxide must be regenerated which is also time consuming and not straightforward. The use of cerium (IV) compounds with a noble metal catalyst to oxidize thallium (I) to thallium (III) is probably effective but such procedure requires the regeneration of the cerium (IV) compound which is not economical to do (such requires the use of electro-chemical methods to regenerate cerium (IV) ions).
Also of interest is Belgium Patent No. 855,127 (equivalent to German Offenlegungsschrift No. 27 24,190) which discloses the use of hydroperoxides or molecular oxygen with a noble metal catalyst (e.g., platinum metal) and an amine promoter to oxidize thallium (I) to thallium (III). However, this process with molecular oxygen requires expensive catalysts, extreme conditions of pressure and/or temperature long reaction times, and the like, to obtain relatively low yields (under 65%) of thallium (III) ion products, unless autoclaves or other high-pressure equipment are used. The Belgian and German reference process with hydroperoxides allows good yields to be obtained but again, expensive catalysts and the presence of amine promoters are required as are moderate reaction times (1-19 hours), which limit the utility of these processes for use in a catalytic sense.
There is a need in the catalytic oxidation chemical process art for a process for oxidizing thallium (I) to thallium (III) ions under mild conditions to obtain more quickly essentially quantitative yields using relatively low cost, non-complex equipment, and to produce thallium (III) ions in such form that the thallium (III) ion product can be used more directly in a variety of subsequent oxidation or other chemical operations without contaminating such subsequent products with materials from the thallium (III) reaction mixture.